1. Field of Invention
The present invention relates to a dispensing device for dispensing a preferably medical formulation, in particular containing or consisting of a drug or mixture of drugs.
2. Description of Related Art
Drugs delivered through dispensing devices, in particular inhalers, are intended to optimally target specific sites in the pulmonary system. These sites include the nasal passages, the throat, and various locations within the lungs, such as the bronchi, bronchioles and alveolar regions. The ability to deliver drugs to a target area depends inter alia on the aerodynamic sizes of the particles or droplets. As currently believed to be understood, particles having an aerodynamic diameter of less than 2 micrometer are considered to be potentially optimal for deposition in the alveolar region of the lung. Particles that have an aerodynamic diameter of between 2 and approximately 5 micrometer may be more suitable for delivery to the bronchiole or bronchi regions. Particles with an aerodynamic size range greater than 6 micrometer, and more preferably 10 micrometer, are typically suitable for delivery to the laryngeal region, throat or nasal passages.
In most cases, it is desired to achieve a high inhalable fraction and a high delivery efficiency, i.e., the fraction of the initial dose of drug that reaches the desired region, in particular in the lung. This depends on various factors, in particular on the characteristics of the generated spray plume, such as propagation velocity of the plume, particle size and its distribution, fraction of small particles, fraction of gas or the like. In the present invention, the desired spray plume characteristics include preferably a small particle size, a high fraction of drug particles with a diameter of 6 micrometer or less, a low propagation velocity and/or a long duration of spray generation and possible inhalation.
Most powder inhalers are of the passive type where the powder is inhaled by the patient without the aid of an additional energy source. The problem with passive inhalers is that the inhalable fraction, or the proportion of powder that actually enters the lungs, is largely dependent on the breathing of the patient. The transfer and de-agglomeration of the powder and hence the inhalable fraction is a function of the flow rate of inhaled air through the device and, therefore, varies greatly from patient to patient.
Dry powder inhalers are subdivided into single dose and multi-dose devices or inhalers. Multi-dose inhalers are further subdivided into pre-metered types where the doses are stored individually and into metering inhalers where each powder dose is metered in the device.
Multi dose pre-metered inhalers have the advantage that the single doses are metered under strict factory conditions and the powder can quite easily be isolated from the atmosphere. In many applications the active drug powder is mixed with a carrier such as lactose. The lactose and/or active drug(s) tend to absorb humidity from the atmosphere, which makes them stick together and difficult to transfer and de-agglomerate.
The present invention relates in particular to an active, gas (preferably air) powered, pre-metered multi-dose dispensing device for dispensing a formulation containing or consisting of a drug, such as a dry powder inhaler.
U.S. Pat. No. 4,627,432 A discloses a device for administering medicaments to patients, namely an inhaler. The inhaler comprises a disk-like blister pack having a plurality of blister pockets arranged in a circle. Each blister pocket contains a dose of the powder. A plunger can open a blister pocket. When a blister is opened, the medicament can be withdrawn by a patient inhaling through a mouthpiece.
International Patent Application Publication 2005/002654 A2 discloses a passive device for dispensing individual doses of powder. The doses are contained in respective pockets of a disc-shaped carrier and opened by outwardly rupturing a lidding foil in axial direction by means of pressure on an opposite side surface. The pockets are moveable in axial direction into an airstream generated by breathing of a patient for dispensing a dose of powder from the pocket. The device provides individual respective deaggregation flow paths for each pocket, split airstreams allowing improved entrainment of powder, a cam mechanism for outwardly rupturing the pockets, an indexing mechanism linked to the cam mechanism, and a dose counter.
It is difficult to empty the respective pocket completely during a dispensing operation. Incomplete emptying results in decreased delivery efficiency. Some powder may be lost in the inhaler and not dispensed because the known solutions require relatively long paths for the powder until the powder reaches a nozzle and is actually dispensed. This might reduce the delivery efficiency further. In addition, de-agglomeration of the powder is difficult.
International Patent Application Publication WO 2006/037636 A2 discloses an active dispensing device with an air pump for dispensing powder separately from storage chambers in a common carrier. Preferably, an individual deaggregation and outlet duct having a flat cross-section is associated to each storage chamber.